双层堤基的井涌破坏与无害管涌

双层堤基水文地质结构特殊，堤基承压水常具独特的“渗而不流”特征。在“不流”条件下，堤后盖层薄弱处受超高承压水头顶裂破坏，产生的局部冒水孔实属承压自流井，由此形成的管涌实质为井涌。底部进水的承压井流影响范围不大，井涌的破坏范围更小，据此可区分出有害管涌与无害管涌。前者局限于堤脚附近，小范围压渗为首选方案；对后者，既无需专门防治，更不必追求根治。

Failure by Hole Blow and Harmless Piping in Double Dyke Foundation

Double dyke foundation is special in hydrogeoogic structure. Confined water in the foundation is characterized by leaking without flowing. Given the non_flowing condition, the banket behind the dyke will be broken at thinner and weaker places by jacking of extraordinary high head of confined water. The arising holes where water blows out are actually confined artesian wells and the piping brought about is hole blow in nature. Flow of confined wells where water enters from bottom does not affect more area and damage caused by hole blow is much less. According to this, piping can be classified as harmful and harmless. Harmful piping is confined to near the toe of dyke. For harmless piping, no special treatment is needed, let alone bringing under permanant control.